U.S. patent application number 17/659374 was filed with the patent office on 2022-09-15 for positive electrode active material and method for preparing same.
This patent application is currently assigned to INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY ERICA CAMPUS. The applicant listed for this patent is INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY ERICA CAMPUS. Invention is credited to Dong-Hyung Kim, Jung-Ho Lee, Sambhaji Shivaji Shinde.
Application Number | 20220289571 17/659374 |
Document ID | / |
Family ID | 1000006433044 |
Filed Date | 2022-09-15 |
United States Patent
Application |
20220289571 |
Kind Code |
A1 |
Lee; Jung-Ho ; et
al. |
September 15, 2022 |
POSITIVE ELECTRODE ACTIVE MATERIAL AND METHOD FOR PREPARING
SAME
Abstract
A method for preparing a positive electrode active material is
provided. The method for preparing a positive electrode active
material may comprise the steps of: preparing a lithium precursor,
an iron precursor, a phosphorus precursor, and abase solvent;
mixing the base solvent and the lithium precursor to prepare a
first source, mixing the base solvent and the iron precursor to
prepare a second source, and mixing the base solvent and the
phosphorus precursor to prepare a third source; and mixing the
first source, the second source, the third source, and a chelating
agent and allowing a reaction to occur in the mixture by a heat
treatment method to prepare a positive electrode active material
comprising a compound of lithium, iron, phosphorus, and oxygen.
Inventors: |
Lee; Jung-Ho; (Ansan-si,
KR) ; Shinde; Sambhaji Shivaji; (Ansan-si, KR)
; Kim; Dong-Hyung; (Ansan-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY ERICA
CAMPUS |
Ansan-Si |
|
KR |
|
|
Assignee: |
INDUSTRY-UNIVERSITY COOPERATION
FOUNDATION HANYANG UNIVERSITY ERICA CAMPUS
Ansan-Si
KR
|
Family ID: |
1000006433044 |
Appl. No.: |
17/659374 |
Filed: |
April 15, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/KR2020/014081 |
Oct 15, 2020 |
|
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|
17659374 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01B 25/375 20130101;
C01P 2002/54 20130101; C01P 2002/74 20130101; H01M 10/0525
20130101; H01M 10/0562 20130101 |
International
Class: |
C01B 25/37 20060101
C01B025/37; H01M 10/0562 20060101 H01M010/0562; H01M 10/0525
20060101 H01M010/0525 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 15, 2019 |
KR |
10-2019-0127836 |
Claims
1. A method for preparing a functional positive electrode active
material, the method comprising: providing a first stock solution
in which a base positive electrode active material including a
compound of lithium, iron, phosphorus, and oxygen is dispersed in a
first solvent; providing a second stock solution in which graphene
powder is dispersed in a second solvent; and preparing a functional
positive electrode active material in which the graphene powder is
doped into the base positive electrode active material by mixing
and heat-treating the first stock solution and the second stock
solution.
2. The method of claim 1, wherein the providing of the second stock
solution comprises: preparing a graphene colloid having the
graphene powder by mixing the graphene powder with an oxidizing
agent and heat-treating the mixture; obtaining the graphene powder
from the graphene colloid; and dispersing the graphene powder in
the second solvent.
3. The method of claim 2, wherein the oxidizing agent is hydrogen
peroxide.
4. The method of claim 1, wherein the first solvent and the second
solvent are a same solvent.
5. The method of claim 4, wherein the first solvent and the second
solvent comprises N-methyl-2-pyrrolidone (NMP).
6. A functional positive electrode active material comprising: a
base positive electrode active material including a compound of
lithium, iron, phosphorus, and oxygen; and graphene powder doped
into the base positive electrode active material, wherein a ratio
(I.sub.D/I.sub.G) value of intensity of a D band to intensity of a
G band is greater than 1.98 and less than 3.26 when measuring the
Raman spectrum.
7. The functional positive electrode active material of claim 6,
wherein the graphene powder is 1 at % or more and less than 3 at
%.
8. A lithium secondary battery comprising: a positive electrode
including a functional positive electrode active material according
to claim 6; a negative electrode on the positive electrode; and a
solid electrolyte between the positive electrode and the negative
electrode, wherein the solid electrolyte includes a compound in
which a cation and an anion are bonded.
9. A method for preparing a positive electrode active material, the
method comprising: providing a lithium precursor, an iron
precursor, a phosphorus precursor, and a base solvent; mixing the
base solvent and the lithium precursor to prepare a first source,
mixing the base solvent and the iron precursor to prepare a second
source, and mixing the base solvent and the phosphorus precursor to
prepare a third source; and mixing the first source, the second
source, the third source, and a chelating agent and allowing a
reaction to occur in the mixture by a heat treatment method to
prepare a positive electrode active material including a compound
of lithium, iron, phosphorus, and oxygen.
10. The method of claim 9, wherein the chelating agent comprises at
least any one of pyrrole and citric acid, and a conversion of
Fe.sup.3+ into Fe.sup.2+ is suppressed to suppress a production of
Fe(OH).sub.2 by the chelating agent.
11. The method of claim 9, wherein the lithium precursor comprises
at least any one of Li.sub.2CO.sub.3, LiOH H.sub.2O,
LiH.sub.2PO.sub.4, Li(CH.sub.3COO), LiCl, LiNO.sub.3, lithium
citrate (Li.sub.3C.sub.6H.sub.5O.sub.7) or LiI.
12. The method of claim 9, wherein the iron precursor comprises at
least any one of Fe (NO.sub.3).sub.3, FeSO.sub.4, Fe.sub.2O.sub.3,
FeCl.sub.2 4H.sub.2O, FePO.sub.4, FeC.sub.6H.sub.5O.sub.7, iron
acetate, and iron citrate (FeC.sub.6H.sub.6O.sub.7).
13. The method of claim 9, wherein the phosphorus precursor
comprises at least any one of C.sub.7H.sub.11NO.sub.7P.sub.2,
C.sub.6H.sub.18O.sub.24P.sub.6, (NH.sub.4) .sub.2HPO.sub.4,
H.sub.3PO.sub.4, or LiH.sub.2PO.sub.4.
14. The method of claim 9, wherein the base solvent further
comprises ethylene glycol and deionized water in addition to NMP,
and a volume ratio of ethylene glycol and deionized water is higher
than a volume ratio of the NMP in the base solvent.
15. The method of claim 9, wherein the mixing of the first source,
the second source, the third source, and the chelating agent
comprises: preparing an intermediate product by mixing and reacting
the second source, the third source, and the chelating agent; and
mixing and reacting the intermediate product and the first
source.
16. A lithium secondary battery comprising: a positive electrode
having a positive electrode active material including a compound of
lithium, iron, phosphorus, and oxygen; and a negative electrode on
the positive electrode; and a solid electrolyte between the
positive electrode and the negative electrode.
17. The lithium secondary battery of claim 16, wherein the solid
electrolyte comprises a compound in which a cation and an anion are
bound.
18. The lithium secondary battery of claim 17, wherein the cation
comprises at least any one of thiophenium, thiazolium,
phosphoranium, oxathiolanium, or thiazolidinium, and the anion
comprises at least any one of fluorohydrogenate, cyano
(nitroso)methanide, or tetrazolidine.
19. A positive electrode active material including a compound of
lithium, iron, phosphorus, and oxygen, wherein the positive
electrode active material has a first crystallinity in a state
before charging and discharging of a lithium secondary battery
including the positive electrode active material, and has a second
crystallinity in a state after charging and discharging of the
lithium secondary battery, and the second crystallinity is higher
than the first crystallinity.
20. The positive electrode active material of claim 19, wherein the
second crystallinity is confirmed by using XRD after charging and
discharging of the lithium secondary battery including a solid
electrolyte having a compound in which a cation and an anion are
bound.
Description
TECHNICAL FIELD
[0001] The present application relates to a positive electrode
active material and a method for preparing the same, and more
particularly, to a positive electrode active material including a
compound of lithium, iron, phosphorus, and oxygen and a method for
preparing the same.
BACKGROUND ART
[0002] Small IT devices such as smart phones, etc., took lead in
initial growth of a global secondary battery market, but recently,
a secondary battery market for vehicles is rapidly growing with the
growth of an electric vehicle market.
[0003] Secondary batteries for vehicles are leading the growth of
the electric vehicle market while enabling mass production through
product standardization and achieving low price and stable
performance through technology development, and the market is
rapidly expanding as a short mileage, which was pointed out as a
limitation of electric vehicles, has been resolved by improving
battery performance.
[0004] With an explosive increase in the demand for secondary
batteries, next-generation secondary batteries are also being
actively developed to meet the safety issues of secondary batteries
and the demand for increased battery capacity.
[0005] For example, Korean Unexamined Patent Registration
Publication No. 10-1808373 discloses a positive electrode active
material for a lithium secondary battery, which includes a core
including a particle of lithium transition metal oxide represented
by equation 1 below and a coating layer located on a surface of the
core, in which the coating layer includes niobium (Nb) and the
particle of lithium transition metal oxide of above formula 1 is
doped with tungsten, in which the tungsten is distributed in a
concentration gradient manner that decreases from the surface of
the particle of lithium transition metal oxide to a center thereof:
[Equation 1] Li
(Ni.sub.1-x-y-zMn.sub.xCo.sub.yM.sub.z).sub.aW.sub.l-aO.sub.2 (in
above formula 1, M is selected from the group consisting of Al, Fe,
V, Cr, Ti, Ta, Mg and Mo, and x, y, z and a are
1.ltoreq.x+y+z.ltoreq.1, 0.ltoreq.x<a<1 as an atomic fraction
of independent elements, respectively.).
DISCLOSURE
Technical Problem
[0006] One technical object of the present application is to
provide a positive electrode active material and a method for
preparing the same.
[0007] Another technical object of the present application is to
provide a positive electrode active material including a compound
of lithium, iron, phosphorus, and oxygen and a method for preparing
the same.
[0008] Still another technical object of the present application is
to provide a positive electrode active material capable of
enhancing charge/discharge properties and a method for preparing
the same.
[0009] Still another technical object of the present application is
to provide a positive electrode active material capable of
enhancing high-speed charge/discharge properties and a method for
preparing the same.
[0010] Still another technical object of the present application is
to provide a positive electrode active material having high
stability and long life and a method for preparing the same.
[0011] Still another technical object of the present application is
to provide a positive electrode active material, which is easily
mass-produced, and a method for preparing the same.
[0012] The technical objects of the present application are not
limited to the above.
Technical Solution
[0013] To solve the above technical objects, the present
application may provide a method for preparing a positive electrode
active material.
[0014] According to one embodiment, the method for preparing a
positive electrode active material may include: providing a lithium
precursor, an iron precursor, a phosphorus precursor, and a base
solvent; mixing the base solvent and the lithium precursor to
prepare a first source, mixing the base solvent and the iron
precursor to prepare a second source, and mixing the base solvent
and the phosphorus precursor to prepare a third source; and mixing
the first source, the second source, the third source, and a
chelating agent and allowing a reaction to occur in the mixture by
a heat treatment method to prepare a positive electrode active
material including a compound of lithium, iron, phosphorus, and
oxygen.
[0015] According to one embodiment, the chelating agent may include
at least any one of pyrrole and citric acid, and a conversion of
Fe.sup.3+ into Fe.sup.2+ may be suppressed to suppress a production
of Fe(OH).sub.2 by the chelating agent.
[0016] According to one embodiment, the lithium precursor may
include at least any one of Li.sub.2CO.sub.3, LiOH H.sub.2O,
LiH.sub.2PO.sub.4, Li(CH.sub.3C00), LiCl, LiNO.sub.3, lithium
citrate (Li.sub.3C.sub.6H.sub.5O.sub.7) or LiI.
[0017] According to one embodiment, the iron precursor may include
at least any one of Fe(NO.sub.3).sub.3, FeSO.sub.4,
Fe.sub.2O.sub.3, FeCl.sub.2 4H.sub.2O, FePO.sub.4,
FeC.sub.6H.sub.5O.sub.7, iron acetate, and iron citrate
(FeC.sub.6H.sub.6O.sub.7).
[0018] According to one embodiment, the phosphorus precursor may
include at least any one of C.sub.7H.sub.11NO.sub.7P.sub.2,
C.sub.6H.sub.18O.sub.24P.sub.6, (NH.sub.4).sub.2HPO.sub.4,
H.sub.3PO.sub.4, or LiH.sub.2PO.sub.4.
[0019] According to one embodiment, the base solvent may include
N-methyl-2-pyrrolidone (NMP).
[0020] According to one embodiment, the base solvent may further
include ethylene glycol and deionized water in addition to NMP, and
a volume ratio of ethylene glycol and deionized water may be higher
than a volume ratio of the NMP in the base solvent.
[0021] According to one embodiment, the mixing of the first source,
the second source, the third source, and a chelating agent may
include: preparing an intermediate product by mixing and reacting
the second source, the third source, and the chelating agent; and
mixing and reacting the intermediate product and the first
source.
[0022] To solve the above technical objects, the present
application may provide a lithium secondary battery.
[0023] According to one embodiment, the lithium secondary battery
may include a positive electrode having a positive electrode active
material including a compound of lithium, iron, phosphorus, and
oxygen, a negative electrode on the positive electrode, and a solid
electrolyte between the positive electrode and the negative
electrode.
[0024] According to one embodiment, the solid electrolyte may
include a compound in which a cation and an anion are bound.
[0025] According to one embodiment, the cation may include at least
any one of thiophenium, thiazolium, phosphoranium, oxathiolanium,
or thiazolidinium, and the anion may include at least any one of
fluorohydrogenate, cyano(nitroso)methanide, or tetrazolidine.
[0026] To solve the above technical objects, the present
application may provide a positive electrode active material.
[0027] According to one embodiment, the positive electrode active
material may include a compound of lithium, iron, phosphorus, and
oxygen, in which the positive electrode active material has a first
crystallinity in a state before charging and discharging of a
lithium secondary battery including the positive electrode active
material, and has a second crystallinity in a state after charging
and discharging of the lithium secondary battery, in which the
second crystallinity is higher than the first crystallinity.
[0028] According to one embodiment, the first crystallinity and the
second crystallinity of the positive electrode active material may
be confirmed by using XRD.
[0029] According to one embodiment, the second crystallinity may be
confirmed by using XRD after charging and discharging of the
lithium secondary battery including a solid electrolyte having a
compound in which a cation and an anion are bound.
[0030] To solve the above technical objects, the present
application may provide a method for preparing a functional
positive electrode active material.
[0031] According to one embodiment, the method for preparing a
functional positive electrode active material may include:
providing a first stock solution in which a base positive electrode
active material including a compound of lithium, iron, phosphorus,
and oxygen is dispersed in a first solvent; providing a second
stock solution in which graphene powder is dispersed in a second
solvent; and preparing a functional positive electrode active
material in which the graphene powder is doped into the base
positive electrode active material by mixing and heat-treating the
first stock solution and the second stock solution.
[0032] According to one embodiment, the providing of the second
stock solution may include: preparing a graphene colloid having the
graphene powder by mixing the graphene powder with an oxidizing
agent and heat-treating the mixture; obtaining the graphene powder
from the graphene colloid; and dispersing the graphene powder in
the second solvent.
[0033] According to one embodiment, the oxidizing agent may be
hydrogen peroxide.
[0034] According to one embodiment, the first solvent and the
second solvent may be the same solvent.
[0035] According to one embodiment, the first solvent and the
second solvent may include N-methyl-2-pyrrolidone (NMP).
[0036] To solve the above technical objects, the present
application may provide a functional positive electrode active
material.
[0037] According to one embodiment, the functional positive
electrode active material may include a base positive electrode
active material having a compound of lithium, iron, phosphorus, and
oxygen, and graphene powder doped into the base positive electrode
active material, in which a ratio (I.sub.D/I.sub.G) value of
intensity of a D band to intensity of a G band is greater than 1.98
and less than 3.26 when measuring the Raman spectrum.
[0038] According to one embodiment, the graphene powder may be 1 at
% or more and less than 3 at %.
[0039] To solve the above technical objects, the present
application may provide a lithium secondary battery.
[0040] According to one embodiment, the lithium secondary battery
may include a positive electrode having a functional positive
electrode active material according to the embodiment described
above, a negative electrode on the positive electrode, and a solid
electrolyte between the positive electrode and the negative
electrode, in which the solid electrolyte may include a compound in
which a cation and an anion are bound.
[0041] To solve the above technical objects, the present
application may provide a method for preparing a functional
positive electrode active material.
[0042] According to one embodiment, the method for preparing a
functional positive electrode active material may include:
providing a lithium precursor, an iron precursor, a phosphorus
precursor, and a base solvent; mixing the base solvent and the
lithium precursor to prepare a first source, mixing the base
solvent and the iron precursor to prepare a second source, and
mixing the base solvent and the phosphorus precursor to prepare a
third source; and mixing the first source, the second source, the
third source, and a chelating agent and allowing a reaction to
occur in the mixture by a heat treatment method to prepare a
functional positive electrode active material in which graphitic
carbon is coated on a surface of a base positive electrode active
material containing a compound of lithium, iron, phosphorus, and
oxygen.
[0043] According to one embodiment, a conversion of Fe.sup.3+ into
Fe.sup.2+ may be suppressed to suppress a production of
Fe(OH).sub.2 by the chelating agent, and the carbon contained in
the chelating agent may be heat-treated to form the graphitic
carbon.
[0044] According to one embodiment, the first source, the second
source, the third source, and the chelating agent may be mixed, and
then heat-treated in a nitrogen atmosphere.
[0045] According to one embodiment, the method for preparing a
functional positive electrode active material may include:
providing a lithium precursor, an iron precursor, a phosphorus
precursor, and a base solvent; mixing the base solvent and the
lithium precursor to prepare a first source, mixing the base
solvent and the iron precursor to prepare a second source, and
mixing the base solvent and the phosphorus precursor to prepare a
third source; and mixing the first source, the second source, the
third source, a chelating agent and a graphene source and allowing
a reaction to occur in the mixture by a heat treatment method to
prepare a functional positive electrode active material in which
graphene is grown on a surface of a base positive electrode active
material containing a compound of lithium, iron, phosphorus, and
oxygen.
[0046] According to one embodiment, the mixing of the first source,
the second source, the third source, the chelating agent, and a
graphene source may include: preparing an intermediate product by
mixing and reacting the second source, the third source, the
chelating agent, and the graphene source; and mixing and reacting
the intermediate product and the first source.
[0047] According to one embodiment, the preparing of an
intermediate product may include mixing the second source, the
third source, and the graphene source and allowing a reaction to
occur in the mixture by a heat treatment, and adding the chelating
agent.
Advantageous Effects
[0048] The method for preparing a positive electrode active
material according to an embodiment of the present application can
include: mixing abase solvent and a lithium precursor to prepare a
first source, mixing the base solvent and an iron precursor to
prepare a second source, and mixing the base solvent and a
phosphorus precursor to prepare a third source; and mixing the
first source, the second source, the third source, and a chelating
agent and allowing a reaction to occur in the mixture by a heat
treatment method to prepare a positive electrode active material
including a compound of lithium, iron, phosphorus, and oxygen.
[0049] The positive electrode active material including a compound
of lithium, iron, phosphorus, and oxygen may have a long lifespan
and high stability in high-speed charge/discharge, and may be
prepared in high yield by using inexpensive raw materials.
Accordingly, the method for preparing a positive electrode active
material with an easy mass production and less production cost and
time can be provided.
[0050] In addition, the positive electrode active material can have
high charge/discharge properties by configuring a lithium secondary
battery together with the solid electrolyte in which a cations and
an anion are bound.
[0051] Furthermore, the functional positive electrode active
material according to an embodiment of the present application can
include a base positive electrode active material and graphene
powder coated on the base positive electrode active material.
During charging and discharging of a lithium secondary battery
including the functional positive electrode active material, the
graphene powder can not only enhance the conductivity of a positive
electrode, but also function as an active material that occludes
and desorbs lithium ions along with the base positive electrode
active material, thereby enhancing a charge/discharge capacity.
Accordingly, the functional positive electrode active material can
have a high charge/discharge capacity without using nickel, cobalt,
etc., and may also have high stability against high-speed
charge/discharge and a long lifespan.
DESCRIPTION OF DRAWINGS
[0052] FIG. 1 is a flowchart for explaining a method for preparing
a positive electrode active material according to an embodiment of
the present application.
[0053] FIG. 2 is a flowchart for explaining a method for preparing
a functional positive electrode active material according to a
first embodiment of the present application.
[0054] FIG. 3 is a flowchart for explaining a method for preparing
a functional positive electrode active material according to a
second embodiment of the present application.
[0055] FIG. 4 is a flowchart for explaining a method for preparing
a functional positive electrode active material according to a
third embodiment of the present application.
[0056] FIG. 5 is a view for explaining a secondary battery
according to an embodiment of the present application.
[0057] FIG. 6 is a view showing SEM pictures of a positive
electrode active material according to Experimental Example 1-1 of
the present application.
[0058] FIG. 7 is a view showing results of XRD measurement of a
positive electrode active material according to Experimental
Example 1-1 of the present application.
[0059] FIG. 8 is a graph for explaining charge/discharge properties
of a lithium second battery according to Experimental Example 1-1
of the present application.
[0060] FIG. 9 is a view showing SEM pictures of a positive
electrode active material according to Experimental Example 1-2 of
the present application.
[0061] FIG. 10 is a view showing results of XRD measurement of a
positive electrode active material according to Experimental
Example 1-2 of the present application.
[0062] FIG. 11 is a graph for explaining charge/discharge
properties of a lithium second battery according to Experimental
Example 1-2 of the present application.
[0063] FIG. 12 is a graph for explaining life properties of a
lithium second battery according to Experimental Example 1-2 of the
present application.
[0064] FIG. 13 is a view showing SEM pictures of a positive
electrode active material according to Experimental Example 1-3 of
the present application.
[0065] FIG. 14 is a view showing results of XRD measurement of a
positive electrode active material according to Experimental
Example 1-3 of the present application.
[0066] FIG. 15 is a graph for explaining charge/discharge
properties of a lithium second battery according to Experimental
Example 1-3 of the present application.
[0067] FIG. 16 is a graph for explaining life properties of a
lithium second battery according to Experimental Example 1-3 of the
present application.
[0068] FIG. 17 is a view showing SEM pictures of a positive
electrode active material according to Experimental Example 1-4 of
the present application.
[0069] FIG. 18 is a view showing results of XRD measurement of a
positive electrode active material according to Experimental
Example 1-4 of the present application.
[0070] FIG. 19 is a graph for explaining charge/discharge
properties of a lithium second battery according to Experimental
Example 1-4 of the present application.
[0071] FIG. 20 is a graph for explaining life properties of a
lithium second battery according to Experimental Example 1-4 of the
present application.
[0072] FIG. 21 is a view for comparing charge/discharge properties
of a lithium second battery according to Experimental Examples 1-1
to 1-4 of the present application.
[0073] FIG. 22 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-5 of the present application.
[0074] FIG. 23 is a view showing TEM pictures of a functional
positive electrode active material according to Experimental
Example 1-5 of the present application.
[0075] FIG. 24 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-9 of the present application. FIG. 25 is a view showing
SEM pictures of a functional positive electrode active material
according to Experimental Example 1-10 of the present
application.
[0076] FIG. 26 is a view showing pictures of a functional positive
electrode active material according to Experimental Example 1-11 of
the present application.
[0077] FIG. 27 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-6 of the present application.
[0078] FIG. 28 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-7 of the present application.
[0079] FIG. 29 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-8 of the present application.
[0080] FIG. 30 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-12 of the present application.
[0081] FIG. 31 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-13 of the present application.
[0082] FIG. 32 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-14 of the present application.
[0083] FIG. 33 is a view showing results of XRD analysis of a
positive electrode active material according to Experimental
Example 1-5 of the present application.
[0084] FIG. 34 is a view showing results of Raman spectrum of a
functional positive electrode active material having graphene at
various concentrations according to Experimental Example 1-5 of the
present application.
[0085] FIG. 35 is a graph showing a comparison between a base
positive electrode active material according to Experimental
Example 1-5 and a functional positive electrode active material
according to Experimental Example 1-5 of the present
application.
[0086] FIG. 36 is a graph showing a comparison of capacity among
abase positive electrode active material according to Experimental
Example 1-5, a functional positive electrode active material
according to
[0087] Experimental Example 1-5, functional positive electrode
active materials according to Experimental Examples 1-6 to 1-9,
1-12, and 1-13 of the present application, and commercial
LiFePO.sub.4.
[0088] FIG. 37 is a graph for explaining charge/discharge
properties of a lithium second battery including a functional
positive electrode active material according to Experimental
Example 1-5 of the present application.
[0089] FIG. 38 is a graph for explaining life properties of a
lithium second battery including a functional positive electrode
active material according to Experimental Example 1-5 of the
present application.
[0090] FIG. 39 is a differential scanning calorimetry (DSC) graph
showing a compound according to Experimental Example 2-1 and a
solid electrolyte according to Experimental Example 8-3 of the
present application.
[0091] FIG. 40 is a DSC graph showing a compound according to
Experimental Examples 7-1 and 7-2 of the present application.
[0092] FIG. 41 is a view for explaining a crystal structure of a
solid electrolyte according to Experimental Examples 8-1 to 8-3 of
the present application.
[0093] FIG. 42 is a graph showing an ion conductivity of a compound
according to Experimental Example 2-1 and a solid electrolyte
according to Experimental Examples 8-1 to 8-3 of the present
application depending on a temperature.
[0094] FIG. 43 is a view showing pictures of an electrolyte
membrane coated with a solid electrolyte according to Experimental
Example 8-1 of the present application.
MODE FOR INVENTION
[0095] Hereinafter, preferred embodiments of the present
application will be described in detail with reference to the
accompanying drawings. However, the technical idea of the present
application is not limited to the embodiments described herein and
may be implemented in other forms. Rather, the embodiments
introduced herein are provided to sufficiently deliver the spirit
of the present application to those skilled in the art so that the
disclosed contents may become thorough and complete.
[0096] When it is mentioned in the specification that one element
is on another element, it means that the first element may be
directly formed on the second element or a third element may be
interposed between the first element and the second element.
Further, in the drawings, the thicknesses of the membrane and areas
are exaggerated for efficient description of the technical
contents.
[0097] Further, in the various embodiments of the present
specification, the terms such as first, second, and third are used
to describe various elements, but the elements are not limited to
the terms. These terms are used only to distinguish one component
from another component. Accordingly, an element mentioned as a
first element in one embodiment may be mentioned as a second
element in another embodiment. The embodiments described and
illustrated herein also include their complementary embodiments.
Further, the term "and/or" in the specification is used to include
at least one of the elements enumerated in the specification.
[0098] In the specification, the terms of a singular form may
include plural forms unless otherwise specified. Further, the terms
"including" and "having" are used to designate that the features,
the numbers, the steps, the elements, or combinations thereof
described in the specification are present, and are not to be
understood as excluding the possibility that one or more other
features, numbers, steps, elements, or combinations thereof may be
present or added.
[0099] Further, in the following description of the present
application, a detailed description of known functions or
configurations incorporated herein will be omitted when it may make
the subj ect matter of the present application unnecessarily
unclear.
[0100] FIG. 1 is a flowchart for explaining a method for preparing
a positive electrode active material according to an embodiment of
the present application.
[0101] Referring to FIG. 1, a lithium precursor, an iron precursor,
a phosphorus precursor, and a base solvent may be provided
(S110).
[0102] According to one embodiment, the lithium precursor may
include at least any one of Li.sub.2CO.sub.3, LiOH H.sub.2O,
LiH.sub.2PO.sub.4, Li(CH.sub.3COO), LiCl, LiNO.sub.3, lithium
citrate (Li.sub.3C.sub.6H.sub.5O.sub.7) or LiI, the iron precursor
may include at least any one of Fe (NO.sub.3).sub.3, FeSO.sub.4,
Fe.sub.2O.sub.3, FeCl.sub.2 4H.sub.2O, FePO.sub.4,
FeC.sub.6H.sub.5O.sub.7, iron acetate, or iron citrate
(FeC.sub.6H.sub.6O.sub.7), and the phosphorus precursor may include
at least any one of C.sub.7H.sub.11NO.sub.7P.sub.2,
C.sub.6H.sub.18O.sub.24P.sub.6, (NH.sub.4) .sub.2HPO.sub.4,
H.sub.3PO.sub.4, or LiH.sub.2PO.sub.4.
[0103] The base solvent may be a mixed solvent in which a plurality
of solutions are mixed. According to one embodiment, the base
solvent may include N-methyl-2-pyrrolidone (NMP). In this case, the
base solvent may further include ethylene glycol and deionized
water in addition to the NMP, and a volume ratio of ethylene glycol
and deionized water may be higher than a volume ratio of the NMP in
the base solvent. In addition, a volume ratio of ethylene glycol
and deionized water maybe the same. Accordingly, a viscosity of the
base solvent and a solubility of the lithium precursor, the iron
precursor, and the phosphorus precursor may be adjusted.
Specifically, a volume ratio of ethylene glycol and deionized water
may be 0.5 or more and 2 or less, and a volume ratio of the NMP may
be 0.5 or more and 2 or less. For example, a volume ratio of
ethylene glycol, deionized water, and the NMP may be 1:1:0.5.
[0104] As described above, the base solvent used in a process of
preparing the positive electrode active material may include the
NMP. Accordingly, a positive electrode active material including a
compound of lithium, iron, phosphorus, and oxygen, to be described
later, may be uniformly prepared in a small size.
[0105] Unlike the embodiment of the present application described
above, if the base solvent does not contain the NMP, the positive
electrode active material may not have a uniform size, and thus the
charge/discharge properties and lifespan of the secondary battery
including the positive electrode active material maybe
deteriorated.
[0106] However, in the method of preparing the positive electrode
active material according to the embodiment of the present
application, the base solvent may include the NMP, and thus the
positive electrode active material may be uniformly prepared in a
small size, thereby enhancing a charge/discharge capacity of the
secondary battery including the positive electrode active material
and providing a long lifespan thereof.
[0107] Unlike the above, according to another embodiment, the base
solvent may include at least any one of polyol, n-hexane,
acetonitrile, formaldehyde, tetraethyleneglycol, glycerol, or
ethanol.
[0108] The base solvent and the lithium precursor may be mixed to
prepare a first source, the base solvent and the iron precursor may
be mixed to prepare a second source, and the base solvent and the
phosphorus precursor may be mixed to prepare a third source
(S120).
[0109] In other words, as described above, the lithium precursor,
the iron precursor, the phosphorus precursor, and the base solvent
may not be mixed at once, but the base solvent may be accommodated
in three containers, and the lithium precursor, the iron precursor,
and the phosphorus precursor may be mixed in three containers,
respectively, so as to prepare the first to third sources.
[0110] Lithium may function as a reducing agent in a reaction
process to be described later and may be consumed, and thus lithium
may be used in excess. According to one embodiment, a
stoichiometric ratio of lithium, iron, and phosphorus may be 3:1:1
in the first to third sources. Accordingly, a positive electrode
active material including LiFePO .sub.4 to be described later may
be easily prepared.
[0111] The first source, the second source, the third source, and a
chelating agent may be mixed to allow a reaction to occur in the
mixture by a heat treatment method to prepare a positive electrode
active material including a compound of lithium, iron, phosphorus,
and oxygen (S130).
[0112] According to one embodiment, the mixing of the first source,
the second source, the third source, and the chelating agent may
include: preparing an intermediate product by mixing and reacting
the second source, the third source, and the chelating agent; and
mixing and reacting the intermediate product and the first source.
In other words, the intermediate product may be first prepared by
mixing the chelating agent with the second source including iron
and the third source including phosphorus. The intermediate product
may be a compound containing iron and phosphorus . After that, the
positive electrode active material including a compound of lithium,
iron, phosphorus, and oxygen may be prepared by reacting the first
source including lithium with the intermediate product.
[0113] In addition, according to one embodiment, the preparing of
an intermediate product may include mixing the second source
containing iron and the third source containing phosphorus and
allowing a reaction to occur in the mixture by a heat treatment,
and then adding the chelating agent.
[0114] A conversion of Fe.sup.3+ into Fe.sup.2+ may be suppressed
to suppress a production of Fe (OH) .sub.2 by the chelating agent
in a process of preparing the positive electrode active material.
Accordingly, the positive electrode active material including
LiFePO .sub.4, which is a compound of lithium, iron, phosphorus,
and oxygen, may be easily prepared.
[0115] Unlike the embodiment of the present application described
above, in case of not adding the chelating agent, Fe.sup.3+ may be
converted into Fe.sup.2+ to produce Fe (OH) .sub.2 and not to
easily prepare the positive electrode active material including
LiFePO.sub.4, thereby remarkably reducing a production yield.
[0116] According to the embodiment of the present application as
described above, however, the chelating agent may be added after
mixing the second source containing iron and the third source
containing phosphorus and allowing a reaction to occur in the
mixture by a heat treatment, thereby enhancing a manufacturing
yield of the positive electrode active material including
LiFePO.sub.4, which is a compound of lithium, iron, phosphorus, and
oxygen, reducing a production cost, and facilitating a mass
production.
[0117] The positive electrode active material prepared according to
the embodiment of the present application may include a compound of
lithium, iron, phosphorus, and oxygen as described above. In case
of manufacturing a lithium secondary battery by using the positive
electrode active material, crystallinity may not be deteriorated,
but rather may be enhanced, even if charging and discharging of the
lithium secondary battery is performed.
[0118] In other words, when the positive electrode active material
has a first crystallinity in an initial state, that is, before
charging and discharging of the lithium secondary battery including
the positive electrode active material, and the positive electrode
active material has a second crystallinity after charging and
discharging of the lithium secondary battery including the positive
electrode active material (for example, after 500 times of charging
and discharging), the second crystallinity may be higher than the
first crystallinity. According to one embodiment, the first
crystallinity and the second crystallinity may be confirmed by
using an XRD analysis.
[0119] In addition, the lithium secondary battery may use a solid
electrolyte, and in this case, the solid electrolyte may include a
compound in which a cation and an anion are bound. The kind of the
cation and the anion will be described later.
[0120] As such, the crystallographic properties, in which the
crystallinity of the positive electrode active material does not
decrease, but rather increases after charging and discharging, may
be an intrinsic material property resulting from a process of
preparing the positive electrode active material and/or a
combination of the positive electrode active material and the solid
electrolyte according to the embodiment of the present application
as described above.
[0121] According to an embodiment of the present application, the
first source in which the base solvent and the lithium precursor
are mixed, the second source in which the base solvent and the iron
precursor are mixed, the third source in which the base solvent and
the phosphorus precursor are mixed, and the chelating agent maybe
reacted to prepare the positive electrode active material including
a compound of lithium, iron, phosphorus, and oxygen. The positive
electrode active material may have a long lifespan and high
stability in high-speed charging and discharging. In addition, the
positive electrode active material may be prepared in high yield by
using inexpensive raw materials, and thus a method for preparing a
positive electrode active material with an easy mass production and
less production cost and time may be provided.
[0122] In addition, the positive electrode active material may have
high charge/discharge properties by configuring a lithium secondary
battery together with the solid electrolyte in which a cation and
an anion are bound.
[0123] Hereinafter, a functional positive electrode active material
including the positive electrode active material prepared by the
method described with reference to FIG. 1 as a base positive
electrode active material and a method for preparing the same will
be described.
[0124] FIG. 2 is a flowchart for explaining a method for preparing
a functional positive electrode active material according to a
first embodiment of the present application.
[0125] Referring to FIG. 2, a first stock solution, in which a base
positive electrode active material including a compound of lithium,
iron, phosphorus, and oxygen is dispersed in a first solvent, will
be provided (S210).
[0126] According to one embodiment, the preparing of a base
positive electrode active material may include as described with
reference to FIG. 1: providing a lithium precursor, an iron
precursor, a phosphorus precursor, and a base solvent; mixing the
base solvent and the lithium precursor to prepare a first source,
mixing the base solvent and the iron precursor to prepare a second
source, and mixing the base solvent and the phosphorus precursor to
prepare a third source; and mixing the first source, the second
source, the third source, and a chelating agent and allowing a
reaction to occur in the mixture by a heat treatment method to
prepare a positive electrode active material. In other words, the
positive electrode active material described with reference to FIG.
1 may be used as the base positive electrode active material.
[0127] The base positive electrode active material prepared by the
above-described method may be dispersed in the first solvent. The
first solvent may include, for example, the NMP.
[0128] A second stock solution in which graphene powder is
dispersed in the second solvent may be provided (S220).
[0129] The second solvent may be the same as the first solvent. As
described above, for example, the first solvent may include the
NMP.
[0130] The graphene powder maybe synthesized from the graphite
powder or prepared by a method of peeling off the graphite powder.
Specifically, according to one embodiment, the graphene powder may
be prepared by a method of treating the graphite powder with
H.sub.2SO.sub.4, adding and reacting KMnO.sub.4, terminating the
reaction with H.sub.2O.sub.2 and deionized water, and then washing
with HCl. Alternatively, according to another embodiment, the
graphene powder may be prepared by peeling off the graphite powder
with an electrolytic solution containing H.sub.2SO.sub.4 and
deionized water as a working electrode.
[0131] The providing of a second stock solution may include:
preparing a graphene colloid having the graphene powder by mixing
the graphene powder with an oxidizing agent (for example,
H.sub.2O.sub.2) and heat-treating the mixture; obtaining the
graphene powder from the graphene colloid; and dispersing the
graphene powder in the second solvent. Accordingly, the graphene
powder may not be agglomerated, but may be easily and uniformly
dispersed in the second solvent. Thus, as will be described later,
the graphene powder may be uniformly doped on a surface of the base
positive electrode active material, and thus a functional positive
electrode active material having high reliability, long lifespan,
and high charge/discharge properties may be provided.
[0132] The functional positive electrode active material, in which
the graphene powder is doped into the base positive electrode
active material, may be prepared by mixing and heat-treating the
first stock solution and the second stock solution (S230).
[0133] According to one embodiment, the second stock solution
having the graphene powder may be added dropwise to the first stock
solution having the base positive electrode active material and
heat-treated, and thus the graphene powder may be doped into the
base positive electrode active material.
[0134] The functional positive electrode active material according
to an embodiment of the present application may include the base
positive electrode active material and the graphene powder coated
on the base positive electrode active material. During charging and
discharging of a lithium secondary battery including the functional
positive electrode active material, the graphene powder may not
only enhance the conductivity of a positive electrode, but also
function as an active material that occludes and desorbs lithium
ions along with the base positive electrode active material,
thereby enhancing a charge/discharge capacity. Accordingly, the
functional positive electrode active material may have a high
stability against high-speed charge/discharge, a high
charge/discharge capacity, and a long lifespan even without using
nickel, cobalt, etc.,
[0135] According to a second embodiment of the present application,
a functional positive electrode active material and a method for
preparing the same will be described.
[0136] FIG. 3 is a flowchart for explaining a method for preparing
a functional positive electrode active material according to a
second embodiment of the present application.
[0137] Referring to FIG. 3, a lithium precursor, an iron precursor,
a phosphorus precursor, and a base solvent will be provided
(S310).
[0138] The lithium precursor, the iron precursor, the phosphorus
precursor, and the base solvent may be prepared by the same method
as that of preparing the base positive electrode active material
described with reference to FIG. 2.
[0139] The base solvent and the lithium precursor may be mixed to
prepare a first source, the base solvent and the iron precursor may
be mixed to prepare a second source, and the base solvent and the
phosphorus precursor may be mixed to prepare a third source
(S320).
[0140] The first source, the second source, and the third source
may be prepared by the same method as that of preparing the base
positive electrode active material described with reference to FIG.
2.
[0141] The first source, the second source, the third source, and a
chelating agent may be mixed to allow a reaction to occur in the
mixture by a heat treatment method to prepare a functional positive
electrode active material in which graphitic carbon is coated on a
surface of a base positive electrode active material containing a
compound of lithium, iron, phosphorus, and oxygen (S330).
[0142] The same method as that of preparing the base positive
electrode active material described with reference to FIG. 2 may be
performed, except that a concentration of the chelating agent may
be higher. In other words, a concentration ratio of the chelating
agent and the Fe source (e.g., 1:1) in the method for preparing the
functional positive electrode active material according to the
second embodiment of the present application may be higher than a
concentration ratio of the chelating agent and the Fe source (e.g.,
0.5:1) in the method for preparing the base positive electrode
active material described with reference to FIG. 2. In other words,
by the same method as the method for preparing the base positive
electrode active material described with reference to FIG. 2, the
second source, the third source, and the chelating agent may be
mixed and reacted to prepare an intermediate product, and the
intermediate product and the first source may be mixed and
heat-treated in a nitrogen atmosphere (e.g., 600.degree. C.) to
prepare the functional positive electrode active material. In this
case, the preparing of an intermediate product may include mixing
the second source containing iron and the third source containing
phosphorus and allowing a reaction to occur in the mixture by a
heat treatment, and then adding the chelating agent at a high
concentration.
[0143] Accordingly, a conversion of Fe.sup.3+ into Fe.sup.2+ may be
suppressed to suppress a production of Fe(OH).sub.2 by the
chelating agent, and the carbon contained in the chelating agent
may be also heat-treated to form the graphitic carbon.
[0144] According to a third embodiment of the present application,
a functional positive electrode active material and a method for
preparing the same will be described.
[0145] FIG. 4 is a flowchart for explaining a method for preparing
a functional positive electrode active material according to a
third embodiment of the present application.
[0146] Referring to FIG. 4, a lithium precursor, an iron precursor,
a phosphorus precursor, and a base solvent will be provided
(S410).
[0147] The lithium precursor, the iron precursor, the phosphorus
precursor, and the base solvent may be prepared by the same method
as that of preparing the base positive electrode active material
described with reference to FIG. 2.
[0148] The base solvent and the lithium precursor may be mixed to
prepare a first source, the base solvent and the iron precursor may
be mixed to prepare a second source, and the base solvent and the
phosphorus precursor may be mixed to prepare a third source
(S420).
[0149] The first source, the second source, and the third source
may be prepared by the same method as that of preparing the base
positive electrode active material described with reference to FIG.
2.
[0150] The first source, the second source, the third source, a
chelating agent and a graphene source may be mixed to allow a
reaction to occur in the mixture by a heat treatment method to
prepare a functional positive electrode active material in which
graphene is grown on a surface of a base positive electrode active
material containing a compound of lithium, iron, phosphorus, and
oxygen.
[0151] Unlike the method for preparing the base positive electrode
active material described with reference to FIG. 2, the graphene
source may be further added. The graphene source may be one in
which graphene powder is dispersed in a solvent as described with
reference to FIG. 2. In this case, the solvent may be a mixture of
deionized water and ethyl alcohol.
[0152] The mixing of the first source, the second source, the third
source, a chelating agent, and a graphene source may include:
[0153] preparing an intermediate product by mixing and reacting the
second source, the third source, the chelating agent, and the
graphene source; and mixing and reacting the intermediate product
and the first source. In other words, the intermediate product may
be first prepared by mixing the second source including iron, the
third source including phosphorus, and the graphene source with the
chelating agent. The intermediate product may be a compound
containing iron, phosphorus and graphene. After that, the
functional positive electrode active material, in which the
graphene is grown on a surface of the base positive electrode
active material including a compound of lithium, iron, phosphorus,
and oxygen, may be prepared by reacting the first source including
lithium with the intermediate product.
[0154] In addition, according to one embodiment, the preparing of
an intermediate product may include mixing the second source
containing iron, the third source containing phosphorus, and the
graphene source and allowing a reaction to occur in the mixture by
a heat treatment, and then adding the chelating agent.
[0155] The positive electrode active material and the functional
positive electrode active material prepared by the method described
above with reference to FIGS. 1 to 4 maybe used as a positive
electrode of a lithium secondary battery together with a solid
electrolyte. Hereinafter, a secondary battery according to an
embodiment of the present application will be described with
reference to FIG. 5.
[0156] FIG. 5 is a view for explaining a secondary battery
according to an embodiment of the present application.
[0157] Referring to FIG. 5, the secondary battery according to an
embodiment of the present application may include a negative
electrode 210, a solid electrolyte 220, and a positive electrode
230.
[0158] The negative electrode 210 may include various materials
such as a carbon-based material, silicon, lithium, etc.
[0159] For example, the positive electrode 230 may include the
positive electrode active material including a compound of lithium,
iron, phosphorus, and oxygen as described with reference to FIG. 1.
Alternatively, the positive electrode 230 may include the
functional positive electrode active material containing a compound
of lithium, iron, phosphorus, and oxygen as described with
reference to FIGS. 2 to 4. In other words, the positive electrode
active material, a binder, and a conductive material maybe coated
on a current collector to provide the positive electrode 230.
[0160] The solid electrolyte 220 may be a compound in which a
cation and an anion are bound.
[0161] Specifically, the cation may include at least any one of
thiophenium represented by <Formula 1>, thiazolium
represented by <Formula 2>, phospholanium represented by
<Formula 3>, or oxathiolanium represented by <Formula
4> or <Formula 5>, or thiazolidinium represented by
<Formula 6>. In <Formula 1> to <Formula 6>, R1
may be an alkyl group.
##STR00001##
[0162] Specifically, the anion may include fluorohydrogenate
represented by <Formula 7>.
##STR00002##
[0163] Alternatively, the anion may include cyano(nitroso)methanide
or tetrazolidine.
[0164] According to another embodiment, the solid electrolyte 220
may be an oxide, sulfide, or polymer-based material, as described
above.
[0165] Hereinafter, a positive electrode active material prepared
according to a specific experimental example of the present
application, and results of evaluating properties will be described
accordingly.
[0166] Fabrication of Positive Electrode Active Material and
Lithium Secondary Battery according to Experimental Example 1-1
[0167] Li.sub.2CO.sub.3 was provided as a lithium precursor, a
solution, in which risedronic acid (C.sub.7H.sub.11NO.sub.7P.sub.2)
and phytic acid (C.sub.6H.sub.18O.sub.24P.sub.6) were mixed at a
volume ratio of 1:1, was provided as a phosphorus precursor, and
iron nitrate (Fe(NO.sub.3).sub.3) was provided as an iron
precursor.
[0168] A solution, in which ethylene glycol, deionized water and
the NMP were mixed at a volume ratio of 1:1:0.5, was provided as a
base solvent, the base solvent and the lithium precursor were mixed
to prepare a first source, the base solvent and the iron precursor
were mixed to prepare a second source, and the base solvent and the
phosphorus precursor were mixed to prepare a third source, in which
a stoichiometric ratio of lithium, iron, and phosphorus was
3:1:1.
[0169] The third source, in which the phosphorus precursor was
mixed, was mixed in the second source, in which the iron precursor
was mixed, and heat-treated at 60.degree. C. for two hours to
produce an intermediate product, which was then washed with ethanol
and deionized water, and dried at 60.degree. C. for three hours in
a vacuum condition.
[0170] Pyrrole (C.sub.4H.sub.5N) and citric acid
(C.sub.6H.sub.8O.sub.7) were provided as the chelating agent, and
the chelating agent was added so that a molar ratio of the
chelating agent to an iron ion might reach 0.5:1.
[0171] After adding the chelating agent, the first source, in which
the lithium precursor was mixed, was added dropwise, reacted at
150.degree. C. for five hours in the atmosphere, purified, washed
three times with deionized water and ethanol, and dried in a vacuum
at 60.degree. C. to prepare a LiFePO.sub.4 positive electrode
active material according to Experimental Example 1-1.
[0172] A positive electrode active material according to
Experimental Example 1-1, carbon black, and the PVDF were mixed at
95:2.5:2.5(wt %) and coated on a current collector to prepare a
positive electrode.
[0173] A lithium foil was provided as a negative electrode, and a
solid electrolyte according to Experimental Example 8-3 to be
described later was used as a solid electrolyte to prepare a
lithium secondary battery according to Experimental Example
1-1.
[0174] Fabrication of Positive Electrode Active Material and
Lithium Secondary Battery according to Experimental Example 1-2
[0175] The same method was performed as in Experimental Example
1-1, except that LiFePO.sub.4 was purchased from *** and provided
as a positive electrode active material according to Experimental
Example 1-2, and a positive electrode active material according to
Experimental Example 1-2, carbon black, and the PVDF were mixed at
8:1:1(wt %) to prepare a lithium secondary battery according to
Experimental Example 1-2.
[0176] Fabrication of Positive Electrode Active Material and
Lithium Secondary Battery according to Experimental Example 1-3
[0177] The same method was performed as in Experimental Example
1-1, except that LiCoO.sub.2 was provided as a positive electrode
active material according to Experimental Example 1-2, and a
positive electrode active material according to Experimental
Example 1-3, carbon black, and the PVDF were mixed at 8:1:1(wt %)
to prepare a lithium secondary battery according to Experimental
Example 1-3.
[0178] Providing of Positive Electrode Active Material according to
Experimental Example 1-4
[0179] The same method was performed as in Experimental Example
1-1, except that LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2 was
provided as a positive electrode active material according to
Experimental Example 1-3, and a positive electrode active material
according to Experimental Example 1-4, carbon black, and the PVDF
were mixed at 8:1:1(wt %) to prepare a lithium secondary battery
according to Experimental Example 1-4.
[0180] FIG. 6 is a view showing SEM pictures of a positive
electrode active material according to Experimental Example 1-1 of
the present application.
[0181] Referring to FIG. 6, SEM pictures were taken of a positive
electrode active material according to Experimental Example 1-1.
According to the embodiment of the present application, it can be
confirmed that the LiFePO.sub.4 positive electrode active material
is prepared to have a uniform size. In particular, it can be
confirmed that the inventive material has a uniformly small size
and is prepared to be substantially spherical compared to
commercial LiFePO.sub.4 of Experimental Example 1-2 as shown in
FIG. 10 to be described later.
[0182] FIG. 7 is a view showing results of XRD measurement of a
positive electrode active material according to Experimental
Example 1-1 of the present application.
[0183] Referring to FIG. 7, an XRD measurement was performed for a
positive electrode active material according to Experimental
Example 1-1 of the present application. As shown in FIG. 7, it can
be confirmed that a positive electrode active material having a
LiFePO.sub.4 composition is prepared.
[0184] FIG. 8 is a graph for explaining charge/discharge properties
of a lithium second battery according to Experimental Example 1-1
of the present application.
[0185] Referring to FIG. 8, charge/discharge was performed for a
lithium secondary battery according to Experimental Example 1-1
under 1C condition. As shown in FIG. 8, it can be confirmed that
the lithium secondary battery has a high capacity and is stably
driven under the 1C condition.
[0186] FIG. 9 is a view showing SEM pictures of a positive
electrode active material according to Experimental Example 1-2 of
the present application.
[0187] Referring to FIG. 9, SEM pictures were taken of a positive
electrode active material according to Experimental Example 1-2.
(a) and (b) of FIG. 9 are view showing SEM pictures of a positive
electrode active material in an initial state before charging and
discharging, and (c) and (d) of FIG. 9 are views showing SEM
pictures of a positive electrode active material after 500 times of
charging and discharging of the lithium secondary battery of
Experimental Example 1-2 under 1C condition.
[0188] As can be understood from FIG. 9, due to a combination with
a solid electrolyte in which a cation and an anion are bound along
with a highly stable crystal structure of the LiFePO.sub.4 positive
electrode active material having an olivine crystal structure, it
can be confirmed that the inventive material has substantially the
same morphology as that of the initial state except occurrence of a
fine aggregation even after 500 times of charge/discharge. In
addition, it can be seen that the lithium secondary battery of
Experimental Example 1-2 is driven without crystallographic
deterioration of the positive electrode active material of
Experimental Example 1-2, as the solid electrolyte, in which a
cation and an anion are bound, is combined with the positive
electrode active material of Experimental Example 1-2.
[0189] FIG. 10 is a view showing results of XRD measurement of a
positive electrode active material according to Experimental
Example 1-2 of the present application.
[0190] Referring to FIG. 10, an XRD measurement was performed for a
positive electrode active material according to Experimental
Example 1-2. Specifically, an XRD measurement was performed for the
positive electrode active material in an initial state before
charging and discharging, and an XRD measurement was performed for
the positive electrode active material after 500 times of charging
and discharging of the lithium secondary battery of Experimental
Example 1-2 under 1C condition.
[0191] As can be understood from FIG. 10, it can be confirmed that
an initial crystal structure of the positive electrode active
material of Experimental Example 1-2 is maintained to be
substantially the same even after 500 times of charging and
discharging. In addition, it can be confirmed that an intensity of
peak values is rather increased as a whole. In other words, it can
be seen that a crystallinity of the positive electrode active
material is rather increased after charging and discharging. As
such, it can be interpreted that an increase in crystallinity after
charging and discharging is an unique crystallographic/material
property due to a combination between the solid electrolyte
according to the embodiment of the present application including a
compound, in which a cation and an anion are bound according to the
embodiment of the present application, and LiFePO.sub.4 positive
electrode active material.
[0192] FIG. 11 is a graph for explaining charge/discharge
properties of a lithium second battery according to Experimental
Example 1-2 of the present application, and FIG. 12 is a graph for
explaining life properties of a lithium second battery according to
Experimental Example 1-2 of the present application.
[0193] Referring to FIGS. 11 and 12, charge/discharge was performed
500 times for a lithium secondary battery according to Experimental
Example 1-2 under 1C and 10C conditions.
[0194] In case of using the LiFePO.sub.4 positive electrode active
material of Experimental Example 1-2, it can be confirmed that the
battery has a high capacity of 163 mAhg.sup.-1 and 145.5
mAhg.sup.-1, respectively, under 1C and 10C conditions, and has a
high retention property of 96% and 87% or more even after 500 times
of charging/discharging.
[0195] In particular, as can be understood from FIG. 12, in case of
charging and discharging under 1C condition, it can be confirmed
that coulombic efficiency maintains a high value of 99.8% or more
even after 500 times of charging and discharging.
[0196] In other words, it can be seen that the solid electrolyte
including a cation and an anion prepared according to the
embodiment of the present application is combined with the
LiFePO.sub.4 positive electrode active material to realize high
charge/discharge properties and long life properties.
[0197] FIG. 13 is a view showing SEM pictures of a positive
electrode active material according to Experimental Example 1-3 of
the present application.
[0198] Referring to FIG. 13, SEM pictures were taken of a positive
electrode active material according to Experimental Example 1-3.
(a) and (b) of FIG. 13 are view showing SEM pictures of a positive
electrode active material in an initial state before charging and
discharging, and (c) and (d) of FIG. 13 are views showing SEM
pictures of a positive electrode active material after 500 times of
charging and discharging of the lithium secondary battery of
Experimental Example 1-3 under 1C condition.
[0199] As can be understood from FIG. 13, in case of the lithium
secondary battery of Experimental Example 1-3 including a
LiCoO.sub.2 positive electrode active material having a
rhombohedral crystal structure, it was observed that secondary
protrusions are grown again along a specific direction on a surface
of the positive electrode active material after 500 times of
charging and discharging, and it can be seen that a crack occurs to
the surface of the positive electrode active material after 500
times of charging and discharging.
[0200] FIG. 14 is a view showing results of XRD measurement of a
positive electrode active material according to Experimental
Example 1-3 of the present application.
[0201] Referring to FIG. 14, an XRD measurement was performed for a
positive electrode active material according to Experimental
Example 1-3. Specifically, an XRD measurement was performed for the
positive electrode active material in an initial state before
charging and discharging, and an XRD measurement was performed for
the positive electrode active material after 500 times of charging
and discharging of the lithium secondary battery of Experimental
Example 1-3 under 1C condition.
[0202] As can be understood from FIG. 14, it can be confirmed that
an initial crystal structure of the positive electrode active
material of Experimental Example 1-3 is maintained to be
substantially the same even after 500 times of charging and
discharging.
[0203] FIG. 15 is a graph for explaining charge/discharge
properties of a lithium second battery according to Experimental
Example 1-3 of the present application, and FIG. 16 is a graph for
explaining life properties of a lithium second battery according to
Experimental Example 1-3 of the present application.
[0204] Referring to FIGS. 15 and 16, charge/discharge was performed
500 times for a lithium secondary battery according to Experimental
Example 1-3 under 0.1C, 0.5C and 1C conditions.
[0205] In case of using the LiCoO.sub.2 positive electrode active
material of Experimental Example 1-3, it can be confirmed that the
battery has a capacity of 209 mAhg-1 and 201 mAhg-1, respectively,
under 0.1C and 1C conditions. In case of charging and discharging
under 1C condition, it can be seen that the battery has a coulombic
efficiency of 99.7% and maintains a capacity of 96% compared to an
initial capacity even after 500 times of charging/discharging.
[0206] In other words, it can be seen that the solid electrolyte
including a cation and an anion prepared according to the
embodiment of the present application is combined with the
LiCoO.sub.2 positive electrode active material to realize high
charge/discharge properties and long lifespan properties.
[0207] FIG. 17 is a view showing SEM pictures of a positive
electrode active material according to Experimental Example 1-4 of
the present application.
[0208] Referring to FIG. 17, SEM pictures were taken of a positive
electrode active material according to Experimental Example 1-4.
(a) and (b) of FIG. 17 are view showing SEM pictures of a positive
electrode active material in an initial state before charging and
discharging, and (c) and (d) of FIG. 17 are views showing SEM
pictures of a positive electrode active material after 500 times of
charging and discharging of the lithium secondary battery of
Experimental Example 1-4 under 1C condition.
[0209] As can be understood from FIG. 17, it can be confirmed that
a crack occurs to a surface of a
LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2 positive electrode active
material having a rhombohedral crystal structure and the surface
becomes smooth. In other words, it can be confirmed that a crystal
of the LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2 positive electrode
active material having a layered structure with low stability
collapses during charging and discharging.
[0210] In conclusion, it can be seen that the
LiNi.sub.0.6CO.sub.0.2Mn.sub.0.2O.sub.2 positive electrode active
material of Experimental Example 1-4 has relatively low
crystallographic stability compared to the LiFePO.sub.4 positive
electrode active material of Experimental Example 1-1.
[0211] FIG. 18 is a view showing results of XRD measurement of a
positive electrode active material according to Experimental
Example 1-4 of the present application.
[0212] Referring to FIG. 18, an XRD measurement was performed for a
positive electrode active material according to Experimental
Example 1-4. Specifically, an XRD measurement was performed for the
positive electrode active material in an initial state before
charging and discharging, and an XRD measurement was performed for
the positive electrode active material after 500 times of charging
and discharging of the lithium secondary battery of Experimental
Example 1-4 under 1C condition.
[0213] As can be understood from FIG. 18, it can be confirmed that
an initial crystal structure of the positive electrode active
material of Experimental Example 1-4 is maintained to be
substantially the same even after 500 times of charging and
discharging. However, in case of the positive electrode active
material of Experimental Examples 1-4, it can be seen that an
overall peak value is decreased and crystallinity is decreased due
to the charging and discharging.
[0214] FIG. 19 is a graph for explaining charge/discharge
properties of a lithium second battery according to Experimental
Example 1-4 of the present application, and FIG. 20 is a graph for
explaining life properties of a lithium second battery according to
Experimental Example 1-4 of the present application.
[0215] Referring to FIGS. 19 and 20, charge/discharge was performed
500 times for a lithium secondary battery according to Experimental
Example 1-4 under 1C, 2C and 3C conditions.
[0216] In case of using the LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2
positive electrode active material of Experimental Example 1-4, it
can be confirmed that the battery has a high capacity of 231
mAhg.sup.-1 under 1C condition, and it can be seen that the battery
has a high retention property of 99.8% or more even after 500 times
of charging/discharging. In addition, it can be seen that the
battery has a high retention property of 90% and 88%, respectively,
even after 500 times of charging and discharging even under 2C and
3C conditions.
[0217] In case of not using the solid electrolyte as in an
embodiment of the present application, considering that a secondary
battery using a LiNi.sub.0.6CO.sub.0.1Mn.sub.0.1O.sub.2 positive
electrode active material generally exhibits a capacity of about
210 mAh/g-1 and a secondary battery using a
LiNi.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2 positive electrode active
material has a capacity of about 230 mAhg-1, it can be seen that
the solid electrolyte including a cation and an anion prepared
according to an embodiment of the present application is combined
with a positive electrode active material containing nickel,
cobalt, and manganese to realize high charge and discharge
properties. In other words, incase of using the solid electrolyte
as in an embodiment of the present application, it can be confirmed
that it is possible to implement charge/discharge properties
substantially similar to those of using a positive electrode active
material having a relatively high nickel concentration, even when
using a positive electrode active material having a relatively low
nickel concentration.
[0218] FIG. 21 is a view for comparing charge/discharge properties
of a lithium second battery according to Experimental Examples 1-1
to 1-4 of the present application.
[0219] Referring to FIG. 21, a comparison was made fora capacity
among the lithium secondary batteries according to Experimental
Examples 1-1 to 1-4.
[0220] In case of including the LiFePO.sub.4 positive electrode
active material prepared according to Experimental Example 1-1, it
can be confirmed that the battery has a capacity higher than that
of including the LiFePO.sub.4 positive electrode active material
according to Experimental Example 1-2 sold in the market.
[0221] In addition, it can be confirmed that a solid electrolyte
having a compound in which an cation and an anion are bound may be
used with a positive electrode active material at various
compositions such as LiFePO.sub.4, LiCoO.sub.2,
LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2.
[0222] Hereinafter, a functional positive electrode active material
prepared according to a specific experimental example of the
present application, and results of evaluating properties will be
described accordingly.
[0223] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-5
[0224] A positive electrode active material according to
Experimental Example 1-1 was used as a base positive electrode
active material and dispersed in the NMP to prepare a first stock
solution.
[0225] After graphite powder was treated with H.sub.2SO.sub.4 at a
high concentration, and KMnO.sub.4 was added at 0.degree. C. After
that, the mixture was reacted at 35.degree. C. for 30 minutes and
reacted at 98.degree. C. for 15 minutes. The reaction was
terminated by adding 30% H.sub.2O.sub.2 and 500 ml of deionized
water, filtered, and washed with HCl (1:10) to remove unreacted
metal ions and acids. After that, the obtained product was washed
with deionized water and dried to synthesize graphene powder.
[0226] Then, the graphene powder was dispersed in the NMP to
prepare a second stock solution in which the graphene powder was
dispersed.
[0227] The second stock solution, in which the graphene powder was
dispersed, was added dropwise to the first stock solution having
the base positive electrode active material and reacted at
200.degree. C. for one hour, so as to prepare a functional positive
electrode active material according to Experimental Examples 1-5,
in which the graphene powder was doped into the LiFePO.sub.4-based
positive electrode active material while adjusting a ratio of the
graphene powder at 1 at %, 2 at %, 3 at %, 5 at %, and 10 at %.
[0228] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-6
[0229] Graphite was used as a working electrode, and deionized
water, in which H.sub.2SO.sub.4 was dissolved, was used as an
electrolytic solution to peel off the graphite at 10. 5V for eight
minutes, thereby preparing graphene powder.
[0230] Then, the graphene powder was dispersed in the NMP to
prepare a second stock solution in which the graphene powder was
dispersed.
[0231] After that, the second stock solution, in which the graphene
powder was dispersed, was added dropwise to the first stock
solution having the base positive electrode active material
prepared according to Experimental Example 1-5 and reacted at
200.degree. C. for one hour, so as to prepare a functional positive
electrode active material according to Experimental Examples 1-6,
in which the graphene powder of 2 at % was doped into the
LiFePO.sub.4-based positive electrode active material.
[0232] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-7
[0233] A base positive electrode active material was prepared by
the same method as in Experimental Example 1-5, except for doubling
a concentration of a chelating agent compared with the method for
preparing the base positive electrode active material as described
in Experimental Examples 1-5 in order to use the chelating agent as
a carbon source. After that, a first source, in which a lithium
precursor was mixed, was added dropwise and heat-treated at
600.degree. C. for two hours in a nitrogen atmosphere, so as to
prepare a functional positive electrode active material, in which
graphitic carbon was coated on a surface of the LiFePO.sub.4-based
positive electrode active material according to Experimental
Examples 1-7.
[0234] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-8
[0235] Graphene powder was synthesized by the same method as in
Experimental Examples 1-5. A graphene source was prepared by mixing
the graphene powder with the base solvent of Experimental Examples
1-5.
[0236] A second source, in which an iron precursor was mixed, was
mixed in a third source, in which a phosphorus precursor was mixed,
by the same method as in Experimental Example 1-5, except for
mixing with a graphene source, and then heat-treated at 60.degree.
C. for two hours to produce an intermediate product, which was then
washed with ethanol and deionized water, and dried at 60.degree. C.
for three hours in a vacuum condition.
[0237] After that, a functional positive electrode active material,
in which graphene was grown on a surface of the LiFePO.sub.4-based
positive electrode active material according to Experimental
Examples 1-8, was prepared by performing the same method as the
method for preparing the base positive electrode active material of
Experimental Example 1-5.
[0238] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-9
[0239] A functional positive electrode active material according to
Experimental Examples 1-9, in which the graphene powder of 2 at %
was doped into the LiFePO.sub.4-based positive electrode active
material, was prepared by performing the same method as in
Experimental Example 1-5, except for using ethylene glycol and
deionized water with the NMP omitted as a base solvent.
[0240] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-10
[0241] A functional positive electrode active material according to
Experimental Examples 1-10, in which the graphene powder of 2 at %
was doped into the LiFePO.sub.4-based positive electrode active
material, was prepared by performing the same method as in
Experimental Example 1-5, except for using ethylene glycol with the
NMP and deionized water omitted as a base solvent.
[0242] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-11
[0243] A functional positive electrode active material according to
Experimental Example 1-11, in which the graphene powder of 2 at %
was doped into the LiFePO.sub.4-based positive electrode active
material, was prepared by performing the same method as in
Experimental Example 1-5, except for using deionized water with the
NMP and ethylene glycol omitted as a base solvent.
[0244] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-12
[0245] A functional positive electrode active material according to
Experimental Example 1-12, having graphene of 2 at %, was prepared
simply by physically mixing the base positive electrode active
material prepared according to Experimental Example 1-5 and the
graphene according to Experimental Example 1-5.
[0246] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-13
[0247] A functional positive electrode active material according to
Experimental Example 1-13, having graphene of 2 at %, was prepared
by providing LiFePO.sub.4 purchased from Sigma Aldrich as a base
positive electrode active material and simply by physically mixing
with graphene according to Experimental Example 1-5.
[0248] Preparing of Functional Positive Electrode Active Material
according to Experimental Example 1-14
[0249] A functional positive electrode active material according to
Experimental Example 1-14, in which the graphene powder of 2 at %
was doped into the LiFePO.sub.4-based positive electrode active
material, was prepared by performing the same method as in
Experimental Example 1-5, except for using LiFePO.sub.4 purchased
from Sigma Aldrich as a base positive electrode active
material.
[0250] The functional positive electrode active material according
to Experimental Examples 1-5 to 1-14 are summarized as shown in
<Table 1> below.
TABLE-US-00001 TABLE 1 LiFePO.sub.4-based positive electrode active
Graphene Classification material concentration Functionalization
Experimental NMP, ethylene 1 at % Graphene synthesis Example 1-5
glycol, deionized 2 at % and doping water 3 at % 5 at % 10 at %
Experimental NMP, ethylene 2 at % Graphene peeling Example 1-6
glycol, deionized and doping water Expeimental NMP, ethylene 2 at %
Graphitic carbon Example 1-7 glycol, deionized coating water
Experimental NMP, ethylene 2 at % Graphene growth Example 1-8
glycol, deionized water Experimental NMP omitted 2 at % Graphene
synthesis Example 1-9 and doping Experimental NMP and 2 at %
Graphene synthesis Example 1-10 deionized water and doping omitted
Experimental NMP and ethylene 2 at % Graphene synthesis Example
1-11 glycol omitted and doping Experimental NMP, ethylene 2 at %
Physical mixing Example 1-12 glycol, deionized water Experimental
Commercial 2 at % Physical mixing Example 1-13 LiFePC.sub.4
Experimental Commercial 2 at % Graphene synthesis Example 1-14
LiFePC.sub.4 and doping
[0251] FIG. 22 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-5 of the present application, FIG. 23 is a view showing
TEM pictures of a functional positive electrode active material
according to Experimental Example 1-5 of the present application,
FIG. 24 is a view showing SEM pictures of a functional positive
electrode active material according to Experimental Example 1-9 of
the present application, FIG. 25 is a view showing SEM pictures of
a functional positive electrode active material according to
Experimental Example 1-10 of the present application, and FIG. 26
is a view showing pictures of a functional positive electrode
active material according to Experimental Example 1-11 of the
present application.
[0252] Referring to FIGS. 22 to 26, SEM and TEM pictures were taken
of the functional positive electrode active material (graphene of 2
at %) according to Experimental Example 1-5, and SEM pictures were
taken of the functional positive electrode active materials
according to Experimental Examples 1-9 to 1-11.
[0253] As shown in FIG. 26, incase of using the NMP and ethylene
glycol according to Experimental Example 1-11 and using deionized
water, it can be confirmed that particles of the base positive
electrode active material are not uniform and a size of the base
positive electrode active material is large in a unit of
micrometer.
[0254] In contrast, as shown in FIGS. 22 to 25, in case of
including at least any one of the NMP and ethylene glycol in a
synthesis process of the base positive electrode active material,
it can be confirmed that particles of a uniform size are prepared
as a whole. In addition, as shown in FIG. 22, in case of including
all of the NMP, ethylene glycol and deionized water in a synthesis
process of the base positive electrode active material, it can be
confirmed that small particles having a uniformly small size are
prepared.
[0255] In other words, it can be seen that using a base solvent
including the NMP, ethylene glycol and deionized water in a process
of preparing the LiFePO.sub.4-based positive electrode active
material is an efficient method of preparing particles having a
uniformly small size.
[0256] In addition, as shown in FIG. 23, it can be confirmed that a
graphene layer is formed on a surface of the LiFePO.sub.4-based
positive electrode active material when graphene of 2 at % is
doped. Specifically, it can be confirmed that graphene is formed at
an edge site of the plane 311 of the LiFePO.sub.4-based positive
electrode active material.
[0257] FIG. 27 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-6 of the present application, FIG. 27 is a view showing
SEM pictures of a functional positive electrode active material
according to Experimental Example 1-7 of the present application,
and FIG. 29 is a view showing SEM pictures of a functional positive
electrode active material according to Experimental Example 1-8 of
the present application.
[0258] Referring to FIGS. 27 to 29, SEM pictures were taken of the
functional electrode active materials according to Experimental
Examples 1-6 to 1-8 of the present application.
[0259] As shown in FIG. 27, in case of the functional positive
electrode active material prepared according to Experimental
Example 1-6, it can be confirmed that graphene is not uniformly
distributed, compared to the functional positive electrode active
material prepared according to Experimental Example 1-5 described
with reference to FIG. 22.
[0260] In addition, as shown in FIG. 28, when graphitic carbon is
coated on the LiFePO.sub.4-based positive electrode active material
according to Experimental Example 1-7, it can be seen that
graphitic carbon on a surface of the base positive electrode active
material is synthesized as nanoparticles to make a bond between
LiFePO.sub.4-based positive electrode active materials.
[0261] In addition, as shown in FIG. 29, when graphene is grown on
a surface of the LiFePO.sub.4-based positive electrode active
material according to Experimental Example 1-8, it can be confirmed
that the LiFePO.sub.4-based positive electrode active material is
grown as a non-uniform morphology.
[0262] FIG. 30 is a view showing SEM pictures of a functional
positive electrode active material according to Experimental
Example 1-12 of the present invention, FIG. 22 is a view showing
SEM pictures of a functional positive electrode active material
according to Experimental Example 1-13 of the present invention,
and FIG. 22 is a view showing SEM pictures of a functional positive
electrode active material according to Experimental Example 1-14 of
the present invention.
[0263] Referring to FIGS. 30 to 32, SEM pictures were taken of the
functional electrode active materials according to Experimental
Examples 1-12 to 1-14 of the present application.
[0264] As shown in FIG. 30, when preparing a functional positive
electrode active material simply by mixing the LiFePO.sub.4-based
positive electrode active material according to Experimental
Example 1-12 with graphene, it can be confirmed that the material
is not relatively uniform and has an optional morphology compared
to the functional positive electrode active material according to
Experimental Example 1-5 as shown in FIG. 22.
[0265] As shown in FIG. 31, when using a commercial
LiFePO.sub.4-based positive electrode active material, it can be
confirmed that the material has a relatively non-uniform morphology
compared to not only Experimental Example 1-5, but also
Experimental Example 1-12.
[0266] In addition, as shown in FIG. 32, when using a commercial
LiFePO.sub.4-based positive electrode active material, but doping
with graphene according to an embodiment of the present
application, it can be confirmed that the material has a relatively
non-uniform morphology compared to not only Experimental Example
1-5, but also Experimental Example 1-12.
[0267] FIG. 33 is a view showing results of XRD analysis of a
positive electrode active material according to Experimental
Example 1-5 of the present application, and FIG. 34 is a view
showing results of Raman spectrum of a functional positive
electrode active material having graphene at various concentrations
according to Experimental Example 1-5 of the present invention.
[0268] Referring to FIGS. 33 and 34, an XRD analysis was made for
the functional positive electrode active material having graphene
of 2 at % according to Experimental Example 1-5, and a Raman
spectrum was analyzed for functional positive electrode active
materials having graphene powder of 1 at %, 2 at %, 3 at %, 5 at %
and 10 at % according to Experimental Example 1-5.
[0269] As shown in FIG. 33, it can be confirmed that both the
LiFePO.sub.4-based positive electrode active material of
Experimental Example 1-5 without the addition of graphene powder
and the functional positive electrode active material having
graphene powder of 2 at % according to Experimental Example 1-5
have an orthorhombic crystal structure and a Pnma space group, and
it can be confirmed that the functional positive electrode active
material of Experimental Examples 1-5 has high purity and high
crystallinity and well maintains an initial crystal structure as it
is even after the graphene powder is doped.
[0270] In addition, based on a result of XRD analysis, it was
difficult to confirm a clear difference in a peak with or without
the addition of graphene powder due to Bragg's reflection having
high intensity 111 of the LiFePO.sub.4-based positive electrode
active material.
[0271] As shown in FIG. 34, as a result of Raman spectrum analysis
of pure graphene, LiFePO.sub.4-based positive electrode active
material of Experimental Example 1-5, and the functional positive
electrode active material having graphene powder of 1 at %, 2 at %,
3 at %, 5 at %, and 10 at % according to Experimental Example 1-5,
a vibration of Fe--O and PO.sub.4.sup.3- of the LiFePO.sub.4-based
positive electrode active material may be confirmed in the regions
of 500-700 cm.sup.- and 800-1200 cm.sup.-1, and the disorder/defect
(D) band and graphitic (G) band of graphene were observed in 1259
cm.sup.-1 and 1607 cm.sup.-1 as a peak of high intensity.
[0272] It can be seen that a peak is slightly shifted in the D band
of the functional positive electrode active material doped with
graphene powder, and has a peak value at 1247 cm.sup.-1.
[0273] The broadening of the peak of the D band of the functional
positive electrode active material doped with graphene powder was
the result of stacking a localized in-plane sp2 domain and a
disordered graphitic crystal of graphene, and thus the
charge/discharge capacity of the conductive and positive electrode
active material may be increased.
[0274] In addition, a ratio (I.sub.D/I.sub.G) value of intensity of
the D band to the intensity of the G band according to a
concentration of graphene powder was measured as shown in <Table
2> below.
[0275] As will be described later, when a ratio of graphene powder
in the functional positive electrode active material is more than 1
at % and less than 3 at %, a charge/discharge capacity may be the
highest, and in this case, a ratio of intensity of the D band to
the intensity of the G band (I.sub.D/I.sub.G) value may be greater
than 3.2 and less than 3.26.
TABLE-US-00002 TABLE 2 Ratio of graphene powder I.sub.D/I.sub.G
ratio 1 at % 3.20 2 at % 3.26 3 at % 3.26 5 at % 3.21 10 at %
3.20
[0276] FIG. 35 is a graph showing a comparison between a base
positive electrode active material according to Experimental
Example 1-5 and a positive electrode active material according to
Experimental Example 1-5 of the present application, and FIG. 36 is
a graph showing a comparison of capacity among a base positive
electrode active material according to Experimental Example 1-5, a
functional positive electrode active material according to
Experimental Example 1-5, functional positive electrode active
materials according to Experimental Examples 1-6 to 1-9, 1-12, and
1-13 of the present application, and commercial LiFeFPO.sub.4.
[0277] Referring to FIG. 35, a comparison was made for a capacity
under 1C condition between the base positive electrode active
material according to Experimental Example 1-5 and the functional
positive electrode active material in which a ratio of graphene
powder is 2 at %, 3 at %, 5 at %, and 10 at % according to
Experimental Example 1-5.
[0278] In addition, referring to FIG. 36, a comparison was made for
a capacity under 1C condition among the base positive electrode
active material according to Experimental Example 1-5, the
functional positive electrode active material having 2 at % of
graphene powder according to Experimental Example 1-5, the
functional positive electrode active materials according to
Experimental Examples 1-6 to 1-9, 1-12, and 1-13, and commercial
LiFePO.sub.4.
[0279] As can be understood from FIG. 35, when the graphene powder
is doped, it can be confirmed that the capacity is increased as
compared to the LiFePO.sub.4-based positive electrode active
material of Experimental Examples 1-5. In particular, when a ratio
of the graphene powder is more than 1 at % and less than 3 at %, it
can be confirmed that there is the highest value as 197
mAhg.sup.-1, and when a ratio of the graphene powder is 10 at %,
that is, when exceeding 5 at %, it can be seen that the capacity
rather decreases. Thus, it can be confirmed that doping the
graphene powder to the LiFePO.sub.4-based positive electrode active
material, but controlling a ratio of the graphene powder to 5 at %
or less, preferably controlling the graphene powder to more than 1
at % and less than 3 at %, is an efficient method to enhance a
charge/discharge capacity.
[0280] In addition, as can be understood from FIG. 36, it can be
confirmed that the LiFePO.sub.4-based positive electrode active
material of Experimental Example 1-5 has a high capacity, compared
with the commercial LiFePO.sub.4. When the graphene powder is doped
according to Experimental Example 1-5, it can be confirmed that
there is a high capacity compared to when the graphene powder is
physically mixed as in Experimental Example 1-12.
[0281] In addition, even when the graphene powder is physically
mixed, it can be seen that there is a high capacity when using
LiFePO.sub.4 synthesized according to an embodiment of the present
application as a base positive active material as in Experimental
Examples 1-12 rather than using commercial LiFePO.sub.4 as a base
positive electrode active material as in Experimental Examples
1-13.
[0282] In addition, when doping with the graphene powder
synthesized according to Experimental Example 1-5 or when doping
with the graphene peeled off according to Experimental Example 1-6,
it can be seen that there is a high capacity of 197 mAhg.sup.-1 and
186 mAhg.sup.-1, respectively. In terms of the capacity value, a
theoretical capacity value of LiFePO.sub.4 is higher than 170
mAhg.sup.-1, and it can be confirmed that the doped graphene powder
is directly involved in the occlusion and desorption of lithium
ions, thereby making a contribution as a positive electrode active
material.
[0283] When the LiFePO.sub.4-based positive electrode active
material was coated with graphitic carbon according to Experimental
Example 1-7, it had a capacity of 178 mAhg.sup.-1, which is a
relatively low value compared to Experimental Examples 1-5 and 1-2,
which is understood as a result of enhanced conductivity due to the
graphitic carbon.
[0284] FIG. 37 is a graph for explaining charge/discharge
properties of a lithium second battery including a functional
positive electrode active material according to Experimental
Example 1-5 of the present application, and FIG. 38 is a graph for
explaining life properties of a lithium second battery including a
functional positive electrode active material according to
Experimental Example 1-5 of the present application.
[0285] Referring to FIGS. 37 and 38, a lithium secondary battery
was prepared by using the functional positive electrode active
material doped with graphene powder of 2 at % according to
Experimental Example 1-5, a lithium foil negative electrode, and a
solid electrolyte according to Experimental Example 8-3 to be
described later, and charging and discharging were performed under
0.1C, 0.5C, 1C, 5C, 10C, and 20C conditions.
[0286] It can be seen that the lithium secondary battery including
the functional positive electrode active material according to
Experimental Example 1-5 has a capacity value of 208 mAhg.sup.-1
under 0.1C condition, and it can be confirmed that the battery
maintains a high capacity value of 149 mAhg.sup.-1 even under 20C
condition.
[0287] In addition, it can be confirmed that the battery maintains
a capacity of 89% compared to an initial capacity and has a
coulombic efficiency of 99.6% or more even after 500 times of
charging/discharging under 1C condition.
[0288] Hereinafter, according to specific experimental examples of
the present application, a solid electrolyte including a compound
in which various cations and anions are bound, and results of
evaluating their properties will be described.
[0289] Preparing of Compound according to Experimental Example
2-1
[0290] Acetonitrile was provided into a conical flask, after which
dichloromethane was added and stirred at room temperature for 10
minutes to prepare a solution containing an alkyl group. In this
case, the preparation of the solution containing the alkyl group
was performed in a glove box without moisture.
[0291] Thiophene was dripped into the solution containing the alkyl
group while being stirred, after which a uniformly mixed solution
was slowly stirred at room temperature for four days so as to
prepare thiophenium salt having a methyl group which is a cation
source.
[0292] A washing process was performed by providing the thiophenium
salt and a solvent of ethyl acetate and diethyl ether into a rotary
concentrator.
[0293] 1M hydrofluoric acid and extra water were added into a
conical flask and stirred for 10 minutes to prepare a
fluorohydrogenate precursor which is an anion source.
[0294] Thiophenium salt was added into the fluorohydrogenate
precursor to prepare a mixed solution. The mixed solution was left
alone at a temperature of -70.degree. C. for 24 hours, so as to
prepare a compound in which thiazolium salt and the
fluorohydrogenate were bound as an intermediate product of the
solid electrolyte.
[0295] The compound was provided into a glove box under a nitrogen
atmosphere and left alone at room temperature for two to three
hours, so that volatile gas was removed. After that, a drying
process was performed by providing the compound into the rotary
concentrator, so as to prepare a compound according to Experimental
Example 2-1, in which a thiophenium cation having a methyl group
(R1) and a fluorohydrogenate anion are bound.
[0296] Preparing of Compound according to Experimental Example
2-2
[0297] A compound was prepared by the same method as described
above in Experimental Example 2-1. However, ethyl chloride was
provided instead of dichloromethane. In addition, in the preparing
of thiophenium, a reaction was performed at a temperature of 60 to
80.degree. C. for two to three days instead of the reaction at room
temperature for four days, so as to prepare the compound according
to Experimental Example 2-2, in which a thiophenium cation having
an ethyl group (R1) and a fluorohydrogenate anion are bound.
[0298] Preparing of Compound according to Experimental Example
2-3
[0299] A compound was prepared by the same method as described
above in Experimental Example 2-1. However, propyl chloride was
provided instead of dichloromethane. In addition, in the preparing
of thiophenium, a reaction was performed at a temperature of 60 to
80.degree. C. for two to three days instead of the reaction at room
temperature for four days, so as to prepare the compound according
to Experimental Example 2-3, in which a thiophenium cation having a
propyl group (R1) and a fluorohydrogenate anion are bound.
[0300] Preparing of Compound according to Experimental Example
2-4
[0301] A compound was prepared by the same method as described
above in Experimental Example 2-1. However, butyl chloride was
provided instead of dichloromethane. In addition, in the preparing
of thiophenium, a reaction was performed at a temperature of 60 to
80.degree. C. for two to three days instead of the reaction at room
temperature for four days, so as to prepare the compound according
to Experimental Example 2-4, in which a thiophenium cation having a
butyl group (R1) and a fluorohydrogenate anion are bound.
[0302] Preparing of Compound according to Experimental Example
3-1
[0303] A compound was prepared by the same method as described
above in Experimental Example 2-1, but thiazoline was added into a
solution containing an alkyl group so as to prepare thiazolium salt
as a cation source.
[0304] After that, thiazolium salt and a fluorohydrogenate
precursor were reacted by the same method as described above in
Experimental Example 2-1, so as to prepare the compound according
to Experimental Example 3-1, in which a thiazolium cation having a
methyl group (R1) and a fluorohydrogenate anion are bound.
[0305] Preparing of Compound according to Experimental Example
3-2
[0306] A compound was prepared by the same method as described
above in Experimental Example 2-2, but thiazoline was added into a
solution containing an alkyl group so as to prepare thiazolium salt
as a cation source.
[0307] After that, thiazolium salt and a fluorohydrogenate
precursor were reacted by the same method as described above in
Experimental Example 2-2, so as to prepare the compound according
to Experimental Example 3-2, in which a thiazolium cation having an
ethyl group (R1) and a fluorohydrogenate anion are bound.
[0308] Preparing of Compound according to Experimental Example
3-3
[0309] A compound was prepared by the same method as described
above in Experimental Example 2-3, but thiazoline was added into a
solution containing an alkyl group so as to prepare thiazolium salt
as a cation source.
[0310] After that, thiazolium salt and a fluorohydrogenate
precursor were reacted by the same method as described above in
Experimental Example 2-3, so as to prepare the compound according
to Experimental Example 3-3, in which a thiazolium cation having a
propyl group (R1) and a fluorohydrogenate anion are bound.
[0311] Preparing of Compound according to Experimental Example
3-4
[0312] A compound was prepared by the same method as described
above in Experimental Example 2-4, but thiazoline was added into a
solution containing an alkyl group so as to prepare thiazolium salt
as a cation source.
[0313] After that, thiazolium salt and a fluorohydrogenate
precursor were reacted by the same method as described above in
Experimental Example 2-4, so as to prepare the compound according
to Experimental Example 3-4, in which a thiazolium cation having a
butyl group (R1) and a fluorohydrogenate anion are bound.
[0314] Preparing of Compound according to Experimental Example
4-1
[0315] Phospholanium was provided as a cation, and
fluorohydrogenate prepared according to Experimental Example 2-1 as
described above was used as an anion, so as to prepare the compound
according to Experimental Example 4-1, in which a phospholanium
cation having a methyl group (R1) and an ethyl group (R2) and a
fluorohydrogenate anion are bound.
[0316] Preparing of Compound according to Experimental Example
4-2
[0317] A compound was prepared by the same method as described
above in Experimental Example 4-1, so as to prepare the compound
according to Experimental Example 4-2, in which a phospholanium
cation having a methyl group (R1) and a propyl group (R2) and a
fluorohydrogenate anion are bound.
[0318] Preparing of Compound according to Experimental Example
4-3
[0319] A compound was prepared by the same method as described
above in Experimental Example 4-1, so as to prepare the compound
according to Experimental Example 4-3, in which a phospholanium
cation having a methyl group (R1) and a butyl group (R2) and a
fluorohydrogenate anion are bound.
[0320] Preparing of Compound according to Experimental Example
4-4
[0321] A compound was prepared by the same method as described
above in Experimental Example 4-1, so as to prepare the compound
according to Experimental Example 4-4, in which a phospholanium
cation having an ethyl group (R1) and a butyl group (R2) and a
fluorohydrogenate anion are bound.
[0322] Preparing of Compound according to Experimental Example
4-5
[0323] A compound was prepared by the same method as described
above in Experimental Example 4-1, so as to prepare the compound
according to Experimental Example 4-5, in which a phospholanium
cation having a methyl group (R1) and a methyl group (R2) and a
fluorohydrogenate anion are bound.
[0324] Preparing of Compound according to Experimental Example
5-1
[0325] Oxathiolanium represented by <Formula 8> was provided
as a cation, and fluorohydrogenate prepared according to
Experimental Example 2-1 as described above was used as an anion,
so as to prepare the compound according to Experimental Example
5-1, in which an oxathiolanium cation having a methyl group (R1)
and a fluorohydrogenate anion are bound.
[0326] Preparing of Compound according to Experimental Example
5-2
[0327] A compound was prepared by the same method as described
above in Experimental Example 5-1, so as to prepare the compound
according to Experimental Example 5-2, in which an oxathiolanium
cation having an ethyl group (R1) and a fluorohydrogenate anion are
bound.
[0328] Preparing of Compound according to Experimental Example
5-3
[0329] A compound was prepared by the same method as described
above in Experimental Example 5-1, so as to prepare the compound
according to Experimental Example 5-3, in which an oxathiolanium
cation having a propyl group (R1) and a fluorohydrogenate anion are
bound.
[0330] Preparing of Compound according to Experimental Example
5-4
[0331] A compound was prepared by the same method as described
above in Experimental Example 5-1, so as to prepare the compound
according to Experimental Example 5-4, in which an oxathiolanium
cation having a butyl group (R1) and a fluorohydrogenate anion are
bound.
[0332] Preparing of Compound according to Experimental Example
6-1
[0333] Thiazolidinium was provided as a cation, and
fluorohydrogenate prepared according to Experimental Example 2-1 as
described above was used as an anion, so as to prepare the compound
according to Experimental Example 6-1, in which a thiazolidinium
cation having a methyl group (R1) and an ethyl group (R2) bound to
a nitrogen element, and two methyl groups bound to a sulfur
element, and a fluorohydrogenate anion are bound.
[0334] Preparing of Compound according to Experimental Example
6-2
[0335] A compound was prepared by the same method as described
above in Experimental Example 6-1, so as to prepare the compound
according to Experimental Example 6-2, in which a thiazolidinium
cation having a methyl group (R1) and a propyl group (R2) bound to
a nitrogen element, and two methyl groups bound to a sulfur
element, and a fluorohydrogenate anion are bound.
[0336] Preparing of Compound according to Experimental Example
6-3
[0337] A compound was prepared by the same method as described
above in Experimental Example 6-1, so as to prepare the compound
according to Experimental Example 6-3, in which a thiazolidinium
cation having a methyl group (R1) and a butyl group (R2) bound to a
nitrogen element, and two methyl groups bound to a sulfur element,
and a fluorohydrogenate anion are bound.
[0338] Preparing of Compound according to Experimental Example
6-4
[0339] A compound was prepared by the same method as described
above in Experimental Example 6-1, so as to prepare the compound
according to Experimental Example 8-4, in which a thiazolidinium
cation having an ethyl group (R1) and a butyl group (R2) bound to a
nitrogen element, and two methyl groups bound to a sulfur element,
and a fluorohydrogenate anion are bound.
[0340] The ion conductivity of the compounds according to
Experimental Examples 2-1 to 6-4 was measured at room temperature,
and the ion molecular weight of cations and the state information
of the compounds according to Experimental Examples 2-1 to 6-4 are
summarized as shown in <Table 3>.
TABLE-US-00003 TABLE 3 Ion Ion molecular conduc- Alkyl weight
tivity Classification Cation group (g/mol) State (mS/cm.sup.2)
Experimental Thiophenium Methyl 99.15 Crystalline 126 Example 2-1
group solid Experimental Ethyl 113.14 Crystalline 103 Example 2-2
group solid Experimental Propyl 127.15 Crystalline 68 Example 2-3
group solid Experimental Butyl 142.16 Crystalline 46 Example 2-4
group solid Experimental Thiazolium Methyl 101.13 Crystalline 45
Example 3-1 group solid Experimental Ethyl 114.14 Crystalline 74
Example 3-2 group solid Experimental Propyl 126.15 Crystalline 18.9
Example 3-3 group solid Experimental Butyl 143.13 Crystalline 6.8
Example 3-4 group solid Experimental Phospholanium Methyl 130.97
Crystalline 2 Example 4-1 group/ solid Ethyl group Experimental
Methyl 143.1 Crystalline 35 Example 4-2 group/ solid Propyl group
Experimental Methyl 159.9 Crystalline 16 Example 4-3 group/ solid
Butyl group Experimental Ethyl 174 Crystalline 45 Example 4-4
group/ solid Butyl group Experimental Methyl 117 Crystalline 24
Example 4-5 group/ solid Methyl group Experimental Oxathiolanium
Methyl 106.06 Crystalline 12 Example 5-1 group solid Experimental
Ethyl 120.07 Crystalline 17.5 Example 5-2 group solid Experimental
Propyl 132.06 Crystalline 26.5 Example 5-3 group solid Experimental
Butyl 149.06 Crystalline 21.1 Example 5-4 group solid Experimental
Thiazolidinium Methyl 99.15 Crystalline 60 Example 6-1 group/ solid
Ethyl group Methyl group/ Methyl group Experimental Methyl 113.14
Crystalline 19.6 Example 6-2 group/ solid Propyl group Methyl
group/ Methyl group Experimental Methyl 127.15 Crystalline 28.7
Example 6-3 group/ solid Butyl group Methyl group/ Methyl group
Experimental Ethyl 142.16 Crystalline 5.8 Example 6-4 group/ solid
Butyl group Methyl group/ Methyl group
[0341] As can be understood from <Table 3>, it can be
confirmed that compounds have a high ion conductivity, if
thiophenium is included as a cation (Experimental Examples 2-1 to
2-4), if thiazolium having a methyl group, an ethyl group, or a
propyl group is included (Experimental Examples 3-1 to 3-3), if
phospholanium having a methyl group/propyl group, a methyl
group/butyl group, an ethyl group/butyl group, or a methyl
group/methyl group is included (Experimental Examples 4-2 to 4-5),
if oxathiolanium having an ethyl group, a propyl group, or a butyl
group is included (Experimental Examples 5-2 to 5-4), and if a
thiazolidinium having a methyl group/ethyl group, a methyl
group/propyl group, and a methyl group/butyl group is included
(Experimental Examples 6-1 to 6-3).
[0342] Thiophenium having a methyl group identified as having the
highest ion conductivity in <Table 3> was fixed as a cation
and a type of anion was varied to prepare a compound for a solid
electrolyte according to Experimental Examples 7-1 to 7-2.
[0343] Preparing of Compound according to Experimental Example
7-1
[0344] Cyano(nitroso)methanide was provided as an anion so as to
prepare a compound according to Experimental Example 7-1 in which a
thiophenium cation having a methyl group according to Experimental
Example 2-1 as described above and a cyano(nitroso)methanide anion
are bound.
[0345] Preparing of Compound according to Experimental Example
7-2
[0346] Tetrazolidine was provided as an anion so as to prepare a
compound according to Experimental Example 7-2 in which a
thiophenium cation having a methyl group according to Experimental
Example 2-1 as described above and a tetrazolidine anion are
bound.
[0347] The ion conductivity of the compounds according to
Experimental Examples 7-1 to 7-2 was measured at room temperature,
and the molecular weight of anions, the state information of the
compounds according to Experimental Examples 7-1 to 7-2 are
summarized as shown in <Table 4>.
TABLE-US-00004 TABLE 4 ion Molecular ion weight conductivity
Classification Anion (g/mol) State (mS/cm.sup.2) Experimental
Fluorohydrogenate 63 Crystalline 126 Example 1-1 solid Experimental
Cyano(nitro) 69 Crystalline 48.6 Example 7-1 methanide solid
Experimental Tetrazolidine 72 Crystalline 69.4 Example 7-2
solid
[0348] As can be understood from <Table 4>, it can be
confirmed that compounds have a high ion conductivity, if
fluorohydrogenate is included as an anion (Experimental Example
2-1), if cyano(nitroso)methanide is included (Experimental Example
7-1), and if tetrazolidine is included (Experimental Examples
7-2).
[0349] Preparing of Solid Electrolyte according to Experimental
Example 8-1
[0350] A 1M hydrofluoric acid aqueous solution and lithium chloride
(LiCl) were added into a container and left alone at a temperature
of -70.degree. C. for 24 hours, so as to prepare lithium
fluorohydrogenate.
[0351] A compound having a methyl group according to Experimental
Example 2-1 described above was heated to 60.degree. C. and lithium
fluorohydrogenate was added in an amount of 1 mol % at the same
time and reacted for two hours, so as to prepare a solid
electrolyte according to Experimental Example 8-1.
[0352] Preparing of Solid Electrolyte according to Experimental
Example 8-2
[0353] A solid electrolyte was prepared by the same method as
described above in Experimental Example 8-1. However, lithium
fluorohydrogenate was added in an amount of 5 mol % instead of 1
mol %, so as to prepare a solid electrolyte according to
Experimental Example 8-2.
[0354] Preparing of Solid Electrolyte according to Experimental
Example 8-3
[0355] A solid electrolyte was prepared by the same method as
described above in Experimental Example 8-1. However, lithium
fluorohydrogenate was added in an amount of 10 mol % instead of 1
mol %, so as to prepare a solid electrolyte according to
Experimental Example 8-3.
[0356] FIG. 39 is a differential scanning calorimetry (DSC) graph
showing a compound according to Experimental Example 2-1 and a
solid electrolyte according to Experimental Example 8-3 of the
present application.
[0357] Referring to FIG. 39, a solid-liquid or solid-solid state
change depending on a temperature may be observed in the compound
according to Experimental Example 2-1 and the solid electrolyte
according to Experimental Example 8-3.
[0358] As shown in FIG. 39, a solid-liquid state change was
observed at 90t in the compound of Experimental Example 2-1. In
contrast, a solid-liquid state change was observed at 70.degree. C.
in the solid electrolyte of Experimental Example 8-3.
[0359] In addition, a solid-solid state change was observed twice
in the compound of Experimental Example 2-1, and specifically it
can be seen that the compound of Experimental Example 2-1 has a
first crystal phase in a temperature range of 28 to 90.degree. C.
and a second crystal phase in a temperature range of 22 to
28.degree. C. In contrast, a solid-solid state change was observed
once in the solid electrolyte of Experimental Example 8-3, and it
can be confirmed that the solid electrolyte has one crystal phase
in a temperature range of 22 to 70.degree. C.
[0360] FIG. 40 is a DSC graph showing a compound according to
Experimental Examples 7-1 and 7-2 of the present application.
[0361] Referring to FIG. 40, a state change of compounds according
to Experimental Examples 7-1 and 7-2 was observed depending on a
temperature.
[0362] As can be understood from FIG. 40, it can be confirmed that
the compounds according to Experimental Examples 7-1 and 7-2 stably
maintain a solid crystal phase in a relatively wide range of
temperatures. Specifically, it can be confirmed that the compound
according to Experimental Example 7-1 and the compound according to
Experimental Example 7-2 stably maintain a solid crystal phase -15
to 98.degree. C. and at -59 to 129.degree. C., respectively. In
addition, the compounds according to Experimental Examples 7-1 and
7-2 have a somewhat low ion conductivity compared to the compound
according to Experimental Example 2-1, but stably maintain a
crystal phase in a range of temperatures wider than the range of
temperatures (28 to 90.degree. C.) in which the compound according
to Experimental Example 2-1 stably maintains a first crystal phase
as shown in FIG. 39. Accordingly, the compounds according to
Experimental Examples 7-1 and 7-2 can be useful in military or
space fields, or low-temperature environments such as a polar
region.
[0363] FIG. 41 is a view for explaining a crystal structure of a
solid electrolyte according to Experimental Examples 8-1 to 8-3 of
the present application.
[0364] Referring to FIG. 41, the solid electrolytes according to
Experimental Examples 8-1 to 8-3 may include a thiophenium cation,
a fluorohydrogenate anion and lithium salt.
[0365] A unit cell of the compound in which a thiophenium cation
and a fluorohydrogenate anion are bound may have an orthorhombic
crystal structure, in which the thiophenium cation may be provided
at a vertex of the crystal structure and at a center of a face
thereof, and the fluorohydrogenate anion may be provided in a
middle of an edge of the crystal structure. In this case, the solid
electrolyte of Experimental Examples 8-1 to 8-3 may have the
lithium salt optionally provided at interstitial sites of the
crystal structure. Specifically, the lithium salt may include
lithium fluorohydrogenate.
[0366] The lithium salt may be provided at the interstitial sites
of the crystal structure of the compound, and thus may easily move
within the crystal structure. Accordingly, an ion conductivity may
increase as an addition amount of the lithium fluorohydrogenate,
which is lithium salt, increases.
[0367] FIG. 42 is a graph showing an ion conductivity of a compound
according to Experimental Example 2-1 and a solid electrolyte
according to Experimental Examples 8-1 to 8-3 of the present
application depending on a temperature.
[0368] Referring to FIG. 42, a lithium ion conductivity was
measured with regard to a compound according to Experimental
Example 2-1 and a solid electrolyte according to Experimental
Examples 8-1 to 8-3. As described above with reference to FIG. 41,
lithium fluorohydrogenate may be optionally provided at
interstitial sites in the crystal structure of the compound of the
solid electrolyte of Experimental Examples 8-1 to 8-3. Accordingly,
it was observed that lithium fluorohydrogenate may easily move
within the crystal structure, and thus, when an addition amount of
lithium fluorohydrogenate is increased, an ion conductivity becomes
higher.
[0369] In this case, lithium fluorohydrogenate may move to
interstitial sites in the crystal structure where lithium
fluorohydrogenate is not provided, and may exhibit a high ion
conductivity. Thus, as the interstitial sites provided with lithium
fluorohydrogenate increase, a rate of increase in ion conductivity
may reach saturation. In other words, as shown in FIG. 42, it can
be confirmed that the ion conductivity substantially reaches
saturation, if an addition amount of the lithium fluorohydrogenate
is 5 mol % or more.
[0370] FIG. 43 is a picture of a electrolyte membrane coated with a
solid electrolyte according to Experimental Example 8-1 of the
present application.
[0371] Referring to FIG. 43, a picture was taken of a solid
electrolyte membrane in the form of a film in which a solid
electrolyte according to Experimental Example 8-1 of the present
application is coated on a polytetrafluoroethylene (PTFE) resin. In
this case, it was confirmed that the solid electrolyte membrane
maintains the softness and transparency of the resin.
[0372] Although the present application has been described in
detail with reference to exemplary embodiments, the scope of the
present application is not limited to a specific embodiment and
should be interpreted by the attached claims. In addition, those
skilled in the art should understand that many modifications and
variations are possible without departing from the scope of the
present application.
INDUSTRIAL APPLICABILITY
[0373] A positive electrode active material according to an
embodiment of the present application may be used for a secondary
battery.
* * * * *